The present invention relates to piston type compressors that convert the rotation of a drive shaft to linear reciprocation of pistons by means of drive bodies such as swash plates, and more particularly, to pistons for the same.
A typical compressor includes a crank chamber that is defined in a housing. A drive shaft is rotatably supported in the housing. Part of the housing is constituted by a cylinder block. A plurality of cylinder bores extend through the cylinder block. Each cylinder bore accommodates a piston. A swash plate is fitted to the drive shaft in the crank chamber and supported so as to rotate integrally with the drive shaft. Shoes are provided to couple each piston to the peripheral portion of the swash plate. The swash plate converts the rotation of the drive shaft to linear reciprocation of the pistons. The reciprocation of the pistons compresses refrigerant gas.
There is a type of compressor that has a variable displacement. Such a compressor changes the inclination of the swash plate with respect to the drive shaft. The difference between the pressure in the crank chamber and the pressure in the cylinder bores influences the swash plate through the pistons. Thus, the inclination of the swash plate is determined by the pressure difference. Changes in the inclination of the swash plate alters the stroke of the pistons and varies the displacement of the compressor. In a variable displacement compressor, it is required that the pistons be as light as possible to enable stable control of the displacement under high speed conditions.
Japanese Unexamined Patent Application No. 8-61237 describes a light compressor piston. A generally annular space is provided in the body of each piston. A pair of arms project from the crank chamber end of each piston in a direction substantially perpendicular to the axis of the piston. A groove is defined in the distal end of each arm. A guide rod extends in the axial direction of the pistons between each pair of adjacent cylinder bores. Each guide rod is slidably held between a pair of adjacent arms extending from the associated pair of adjacent pistons. This structure restricts the rotation of each piston. Furthermore, lateral forces applied to each piston (forces acting in a direction perpendicular to the axial direction of the piston) are transmitted through the arms and received by the guide rods.
The inertial force acting on each piston becomes greatest when the piston shifts from the suction stroke to the compression stroke, that is, when the piston becomes close to the bottom dead center. The inertial force of the piston acts on the swash plate. On the other hand, the piston receives reaction force from the swash plate. Due to the inclination of the swash plate, a portion of the reaction force acts in a lateral direction and presses the piston against the wall of the associated cylinder bore. In addition, frictional force is produced between the swash plate and the piston. This produces a further lateral force that tends to incline the piston in the rotating direction of the swash plate. This lateral force also acts in a direction that presses the piston against the wall of the cylinder bore. Such lateral force is transmitted through the associated arms and is received by the guide rods.
In the compressor of the above publication, dimensional differences are produced between the arm grooves and the guide rods when assembling the compressor. To reduce such dimensional differences, the compressor components must be machined accurately. Thus, the machining of these compressor parts is difficult. Furthermore, the guide rods extend through the crank chamber from the front housing and into the cylinder block. The guide rods are fixed to the cylinder block. When installing the guide rods, the guide rods must be inserted through the grooves of opposing arms which is burdensome.
To facilitate the insertion of guide rods between the grooves of opposing arms, a greater clearance may be provided between the wall of the grooves and the guide rods. However, such clearance would result in the guide rods hitting the groove walls when receiving lateral force. This produces undesirable noise.